One senior Mehsud aide, reached by telephone in the Orakzai Agency in northwestern Pakistan, and a local fighter from Mr. Mehsud's area both said that Mr. Mehsud had been receiving kidney treatment from a relative in his father-in-law's house in a remote village in South Waziristan when missiles fired from a remotely piloted drone struck.
The attack took place at 1 a.m. Wednesday, fighters said, while Mr. Mehsud, who was on a drip infusion, was being tended by his wife. Pakistani security officials, who had viewed American footage of the attack, said they were together in an upstairs bedroom.
American officials said Thursday that because the strike took place in a remote area where the military has no access on the ground, confirming the death could take weeks. It may never be possible to perform DNA tests because of the remoteness of the area, the officials said.
The American government made killing or capturing Mr. Mehsud one of its top priorities this year, and his death would boost President Obama's effort to weaken a resurgent Taliban in neighboring Afghanistan.
If Obama personally killed Osama bin Laden and stuck his head on a pike in the White House press room, the right wingers would criticize him for making Mrs. bin Laden a widow.